Molding of precision glass optical elements requires pressing together an upper and lower mold pair. Alignment of this pair is crucial in generating acceptable precision optical components. A prior art molding apparatus 10 as depicted in FIG. 1, and described further in U.S. Pat. No. 4,964,903 titled “Apparatus For Molding Glass Molds” issued Oct. 23, 1990 to Carpenter et al, and U.S. Pat. No. 5,211,969, titled “Mold For Press Molding Of Optical Element” issued May 18, 1993 to Yoshimura, includes an upper mold 1 and a lower mold 3 in a sleeve member 2, so as to be slideable in a longitudinal direction of the sleeve member 2. An upper driving member 4 and a lower driving member 5 provide a force upon the upper mold 1 and lower mold 3. Either one of the driving members 4 or 5 may be stationary, or in the alternative may be movable; thus, providing a degree of concentric alignment. However, alignment limitations exist due to an inherent clearance that allows the molds 1 and 3 to slide between the sleeve member 2. This inherent clearance provides an undesirable potential for tilting and/or shifting of the molds 1 and 3 during a pressing operation which negatively impacts the generated optical element. Translational and concentric error of the molds 1 or 3 may result; thereby, causing misalignment of a work piece's generated surfaces held or formed by the molds 1 and 3.
A second molding apparatus 20 depicted in FIG. 2, and further described in U.S. Pat. No. 5,264,016 titled “Method For Manufacturing Glass Lenses” issued Nov. 23, 1993 to Komiyama; U.S. Pat. No. 5,346,522 titled “Method And Apparatus For Molding Optical Glass Elements Or The Like” issued Sep. 13, 1994 to Komiyama et al.; U.S. Pat. No. 5,282,878 titled “Apparatus For Molding Optical Glass Elements” issued Feb. 1, 1994 to Komiyama et al; U.S. Pat. No. 5,782,946 titled “Method For Manufacturing Press-Molded Glass Object” issued Jul. 21, 1998 to Komiyama et al.; and U.S. Pat. No. 5,938,807 titled “Method For Manufacturing Press-Molded Glass Object And Apparatus Therefor” issued Aug. 17, 1999 to Komiyama et al. includes an upper mold 31 with upper driving member 34 and a lower mold 33 with lower driving member 35. The molding apparatus 20 does not use an external sleeve to provide alignment, as the molding apparatus 10 shown in FIG. 1. Without an external sleeve to provide axial alignment of the upper and lower mold pair 31 and 33, alignment must be achieved through the precision of the apparatus. Members (not shown) that support upper and lower molds 31 and 33 are manufactured incorporating a desired level of concentric alignment and have significant rigidity to perform the pressing operation without distortion. As such, concentric alignment of upper and lower molds 31 and 33 relies upon the ability of a ring member 32 to hold molds 31, 33 concentric to upper and lower driving members 34 and 35 during application of high temperatures. In FIG. 3, an exploded view shows the ring member 32 capable of holding lower mold 33 while in contact with lower driving member 35. The prior art ring member 32, as shown in FIGS. 2, 3, and 4, is simply a rigid round disk with a central hole 40 and may have an additional relief 41 on the underside to provide clearance for retaining features on the molds 31 and 33, such as flanges. During high temperature applications, the diameter of the central hole 40 increases more than the diameter of a cylindrical mold, thereby increasing clearance and loosening the entire assembly. This clearance provides a potential for translational movement between the molds 31 and 33 during the pressing operation which negatively impacts the generated optical element.
What is needed is a molding apparatus with minimal potential for misaligning the upper and lower molds.